IMPACT has following requirements for saving Revit assemblies in the IMPACT database: 

• Assembly should have one element as main and other elements are hosted on the main element. It will define parent and child element relations.
• There should not be any non-hosted elements.    
• Main Element should have level or work plan as a host.
• There should be clarity on how to decide origin or lower left point of element. In that way IMPACT can define correct  placement in the IMPACT database and consequently IMPACT Project Manager.